They indeed did, and that is a correct history of the California Indians. But California was a place that fulfilled the Tlingit proverb of "You have to be an idiot to starve", so there was no need to develop any further (same thing in the Pacific Northwest). It's like the Australian Aboriginals--their way of life worked perfectly, but it could have been so much more if they had transitioned to a fully agricultural model. Were the acorn used by the California natives the path to it? I'm not convinced. Since maize can't be transmitted across the desert, the only solutions to getting agriculture are either indigenous or finding a marooned Japanese/Chinese fisherman to help you do so (which no doubt happened numerous times, since their ships were reported off the coast in colonial times and there's no reason things always weren't that way, even if it was a one way trip). Both are pretty far out hopes, but both are doable when you appeal to human ingenuity. And for indigenous plants, California does have quite a bit, many of which were harvested in their wild form (as wapato was by Californian Indians).